An electric oven is a popular electric heating apparatus for baking food. A conventional electric oven includes a front door, a control panel and a rear shell. Inside the rear shell is an inner chamber where an electric heater and a baking rack are installed. Delicious food is prepared when it is placed on the baking rack and heated with the electric heater. However, it is bothersome for the users after the electric oven is used for some time, because the sludge accumulated on the inner chamber of the oven is very difficult to clean clearly, especially after it is used for baking greasy food. Even if the inner chamber is made of stainless steel or covered with non-stick coatings, the oven is not convenient to clean due to the obstruction of the inner parts secured to the inner chamber, such as the electric heater, etc. Therefore, it is easy to generate bacteria and peculiar smell after the oven is used for some time, which may depress the purchasing desire of some potential customers. To overcome the above mentioned shortcomings, someone designed an integral detachable inner assembly to be installed inside the electric oven. However, the electric heater had to be modified and installed on the back inner board of the oven, which increased the production cost and the whole volume of the oven. In the meantime, the integral detachable inner assembly is too large to be placed into the conventional dish washing troughs or dish washing machines, which brings inconvenience for soaking and washing.